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Project Progress

In collaboration with Emeritus Professor Robert Raiswell of University of Leeds, a group of ASU graduate students (Jen Glass, G. Alex Hamilton, Katie Alexander, Rebecca Mestek, Jennifer Morgan, Jessie Shipp) from the laboratory groups of Hilairy Hartnett, Susanne Neuer and Ariel Anbar performed experiments to investigate the bioavailabilty of iron ferrihydrite nanoparticles to the growth of polar diatoms. Antarctic icebergs are a potential source of Fe to the Southern Ocean, where primary productivity is Fe-limited. Iceberg-hosted sediments contain nanoparticulate Fe oxyhydroxides, of which ferrihydrite is potentially most bioavailable. To investigate the bioavailability of nanoparticulate ferrihydrite, the Arctic pennate diatom Entomoneis sp. CCMP 2396 was grown in artificial seawater containing either synthesized 2-line ferrihydrite (as aggregates of nanoparticles ~ 5 nm diameter), ferric sulfate or no added Fe. Growth rates for the treatment with ferrihydrite nanoparticles were significantly higher than the other two growth conditions. Furthermore, extremely high concentrations of Fe (>2700 ppm) were associated with cells incubated with nanoparticles, suggesting that nanoparticles interact with the cell surface and provide Fe to the cells. These results suggest that nanoparticle Fe is bioavailable and does not require ligand-aided dissolution before uptake. In addition, our findings support the hypothesis that nanoparticulate iceberg Fe fertilizes oceanic productivity in the Southern Ocean today, and may have significantly increased productivity throughout the ocean during the Last Glacial Maximum.